1. Field of the Invention
The present invention relates to a thermosetting resin composition comprising an alkenyl-substituted nadimide, of which the components exhibit excellent compatibility. The composition of the present invention exhibits superior anti-hygroscopicity and superb toughness, and can be used in the absence of a solvent. It is useful as a laminating material, a casting material, a molding material, a coating material, a paint, an adhesive, a sealing material and the like. It is useful also as a matrix resin for composite materials using glass fiber, carbon fiber, or the like as a reinforcing material.
2. Description of the Prior Art
Introduction of allyl group to nadimide which is one of raw materials of thermosetting resins is known to decrease the melting point of the imide raw material, to increase its solubility in solvents, to decrease the setting temperature to a certain degree, and to inhibit generation of volatile compounds when the resin is cured. In addition, the resulting thermosets, i.e., cured materials, are known to exhibit minimal decrease in their properties such as heat resistance, electrical characteristics, mechanical strength, and the like. Thermosets, however, are generally inferior to thermoplastic resins in terms of toughness, and thermosets made from alkenyl-substituted nadimide are no exception. There is a demand for increasing toughness of alkenyl-substituted nadimide as the application of this material expands in recent years. Anti-hygroscopicity is an important characteristic demanded for materials used in the field of electronics and electrical appliances. Polyimides, in general, have high hygroscopicity due to the imide bond, and alkenyl-substituted nadimide also possesses poor anti-hygroscopicity.
Among these characteristics demanded for thermosets, various studies have been undertaken regarding improvement limited to the toughness, and a process recently proposed for increasing the toughness while preserving the high heat resistance is adding a thermoplastic resin with high heat resistance, such as polysulfone, polyether ketone, polyether imide, or aromatic polyester, to epoxy resin. Addition of polyether imide or polyhydantoin to bismaleimide, one of thermosetting polyimide resins, for increasing the toughness has been also proposed [Int. SAMPE Symp., Vol. 33, 1546 (1988)]. Because these thermoplastic resins have poor compatibility with epoxy resin or maleimide resin, a solvent must be used in almost all cases. Because of this circumstance, the application of these resin compositions must be limited to films, thin coatings, or the like from which solvents can be easily vaporized for removal.
A resin composition comprising alkenyl-substituted nadimide and epoxy resin has been developed for the purposes of improving the toughness and anti-hygroscopicity (U.S. Pat. No. 4,579,916). This resin composition has a drawback in that high heat resistance inherently possessed by alkenyl-substituted nadimide is impaired.
More recently, a synthetic resin composition comprising a novolak-type phenol resin, divinylbenzene, and ethylstyrene, having improved toughness and anti-hygroscopicity, has been reported (Japanese Patent Laid-open No. Hei 5 (1993)-117337). This synthetic resin composition has drawbacks still to be improved in its heat resistance, mechanical strength at high temperatures, and molding shrinkage.